After I read the related docuement, I still have no clue how it works and why do we have it.
Could someone understanding it explain it here?
Have you gone through the tutorial chapter on Workflow? That's our best shot at trying to explain it. It's a lot simpler than it may seem at first glance.
Derek, that was the best documentation i found about workflows: https://docs.reactioncommerce.com/reaction-docs/master/workflow